<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>

<body>

    <div id="app">app</div>
    <ul>
        <li class="item">1</li>
        <li class="item">2</li>
        <li class="item">3</li>
        <li class="item">4</li>
        <li class="item">5</li>
    </ul>


    <script>
        var $app = document.querySelector('#app');
        console.log('app', $app);
        var $item = document.querySelector('.item');
        console.log('item', $item);

        var $items = document.querySelectorAll('.item');
        console.log('$items', $items);
    </script>
</body>

</html>